KR20220132471A - Cathode active material for lithium secondary battery, method for preparing thereof, cathode for lithium secondary battery, and lithium secondary battery including the same - Google Patents

Abstract

The present invention provides a high-nickel positive electrode active material which improves stability and initial capacity and suppresses cracks at an interface between primary particles, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery. In addition, the present invention provides a high-nickel positive electrode active material capable of omitting a water washing process by suppressing the content of lithium impurities to a low level, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery.

Description

Positive electrode active material for lithium secondary battery, manufacturing method thereof, positive electrode for lithium secondary battery and lithium secondary battery including same

The present invention relates to a positive active material including a high-nickel (high-Ni)-based lithium transition metal oxide and a method for manufacturing the same.

Demand for high-capacity secondary batteries has recently increased with the development of technologies such as electric vehicles. Accordingly, research on high-nickel (high-Ni)-based positive electrode active materials having excellent capacity characteristics is being actively conducted.

A cathode active material is generally manufactured by mixing a lithium-containing raw material with a transition metal hydroxide and then calcining. When manufacturing a high-nickel-based cathode active material with a high nickel content, the calcination temperature must be low. Residual amounts of lithium by-products such as lithium carbonate and lithium hydroxide increase during the manufacture of the nickel-based positive electrode active material. This lithium by-product reacts with the electrolyte in the secondary battery to deteriorate the performance of the battery and generate gas, and there is a problem in causing a gelation phenomenon in the preparation of the electrode slurry.

Accordingly, in general, when manufacturing a high-nickel-based positive electrode active material, a water washing process is performed to remove lithium byproducts such as lithium carbonate and lithium hydroxide remaining on the particle surface after the firing process. In addition, after the water washing process, boron coating is usually performed to secure stability and initial performance of the positive active material. However, when the boron coating is performed, cracks occur between the primary particles of the lithium transition metal oxide, and when the positive active material is applied to a battery, problems such as gas generation and deterioration of cycle characteristics of the battery occur.

In order to solve this problem, a method of forming a coating layer made of lithium cobalt oxide has been proposed, but in this case, it is difficult to reduce the cost due to the high raw material cost. In addition, when the coating layer made of lithium manganese oxide is formed, there is a disadvantage in that the initial capacity is lowered.

In addition, when the water washing process is performed as described above, lithium by-products are removed, but lithium ions inside the positive active material escape and form NiO, NiOOH, etc. on the surface of the positive active material, resulting in a change in the structure of the lithium transition metal oxide, Accordingly, there is a problem in that the capacity of the lithium secondary battery is reduced.

The present invention is to solve the above problems, it is possible to improve the stability and initial capacity of the lithium secondary battery, the crack generation at the interface between the primary particles is suppressed high-nickel-based positive electrode active material, a method for producing the same, An object of the present invention is to provide a positive electrode and a lithium secondary battery including the same.

In addition, an object of the present invention is to provide a method of manufacturing a high-nickel-based positive electrode active material capable of omitting a water washing process by suppressing the content of lithium by-products to a low level, a positive electrode active material prepared therefrom, a positive electrode including the same, and a lithium secondary battery.

In order to solve the above problems, the present invention provides a positive electrode active material, a method for manufacturing a positive electrode active material, a positive electrode, and a lithium secondary battery.

(1) The present invention is a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and the content of nickel among metal elements other than lithium is 80 atm% or more; a first coating layer formed on the surface of the secondary particles of the lithium transition metal oxide and some or all of the plurality of primary particles, containing nickel and manganese, and having a layered structure; and a second coating layer formed on the outer surface of the first coating layer and containing boron.

(2) The present invention provides a positive electrode active material according to (1), wherein the lithium transition metal oxide has a composition represented by the following formula (1).

[Formula 1]

Li _a Ni _b Co _c M ¹ _d M ² _e O ₂

In Formula 1,

M ¹ is at least one selected from Mn and Al,

M ² is at least one selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y,

0.9≤a≤1.3, 0.8≤b<1.0, 0<c≤0.2, 0<d≤0.2, 0≤e≤0.1.

(3) The present invention provides a positive electrode active material according to (1) or (2), wherein the primary particles have an average particle diameter of 0.1 μm to 0.5 μm.

(4) The present invention provides a positive active material according to any one of (1) to (3), wherein the secondary particles have an average particle diameter (D ₅₀ ) of 8 μm to 15 μm.

(5) The present invention provides a cathode active material according to any one of (1) to (4), wherein the first coating layer has an average thickness of 10 nm to 200 nm.

(6) The present invention provides a cathode active material according to any one of (1) to (5), wherein the first coating layer has a composition represented by the following formula (2).

[Formula 2]

Li _x [Ni _z Mn _w ] _y O ₂

In Formula 2, 0.8≤x≤1.2, 0.8≤y≤1.2, 0.1≤z≤0.9, and 0.1≤w≤0.9.

(7) The present invention provides a cathode active material according to any one of (1) to (6), wherein the molar ratio of nickel to manganese contained in the first coating layer is 1:9 to 9:1.

(8) The present invention provides a cathode active material according to any one of (1) to (7), wherein a molar ratio of nickel to manganese contained in the first coating layer is 5:5 to 9:1.

(9) The present invention provides a cathode active material according to any one of (1) to (8), wherein the first coating layer is included in an amount of 1 to 5 parts by weight based on 100 parts by weight of the lithium transition metal oxide do.

(10) The present invention provides a positive active material according to any one of (1) to (9), wherein the second coating layer includes at least one selected from the group consisting of lithium boron oxide and boron oxide.

(11) The present invention provides a cathode active material according to any one of (1) to (10), wherein the second coating layer is included in an amount of 0.01 part by weight to 1 part by weight based on 100 parts by weight of the lithium transition metal oxide. do.

(12) The present invention provides a cathode active material according to any one of (1) to (11), wherein the content of the lithium by-product remaining on the surface is 1 wt% or less based on the total weight of the cathode active material.

(13) The present invention, a plurality of primary particles in the form of agglomerated secondary particles, the content of nickel among metal elements other than lithium preparing a lithium transition metal oxide of 80atm% or more; A first heat treatment is performed after mixing the lithium transition metal oxide with a solution containing a nickel raw material and a manganese raw material, and the surface of the secondary particles of the lithium transition metal oxide and some or all of the plurality of primary particles Forming a first coating layer containing nickel and manganese on the surface, and having a layered structure; and mixing the lithium transition metal oxide on which the first coating layer is formed with a boron raw material, and performing a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer. to provide.

(14) The present invention provides a method for producing a cathode active material in (13), wherein the preparing of the lithium transition metal oxide is performed by mixing a lithium raw material and a cathode active material precursor and then calcining.

(15) The present invention provides a method for producing a positive electrode active material according to any one of (13) or (14), wherein the preparing of the lithium transition metal oxide does not include a water washing process.

(16) The present invention provides a method for producing a positive electrode active material according to any one of (13) to (15), wherein the nickel raw material is nickel nitrate, and the manganese raw material is manganese nitrate.

(17) The present invention provides a method for producing a positive electrode active material according to any one of (13) to (16), wherein the first heat treatment is performed at 650°C to 850°C.

(18) The present invention provides a method for producing a positive electrode active material according to any one of (13) to (17), wherein the boron raw material is boric acid.

(19) The present invention provides a method for producing a cathode active material according to any one of (13) to (18), wherein the second heat treatment is performed at 150°C to 500°C.

(20) The present invention provides a positive electrode comprising the positive electrode active material of any one of (1) to (12).

(21) The present invention provides a lithium secondary battery comprising the positive electrode, the negative electrode of (20), a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

The high-nickel-based positive active material according to the present invention can improve the stability and initial capacity of a lithium secondary battery, and suppress the occurrence of cracks at the interface between the primary particles, thereby improving the cycle characteristics of the battery.

In addition, according to the method for manufacturing a high-nickel-based positive active material according to the present invention, the water washing process can be omitted by suppressing the content of lithium by-products to a low level, thereby solving the problems caused by the water washing process and reducing equipment and process costs. have.

Accordingly, the high-nickel-based positive electrode active material according to the present invention may be applied to a positive electrode and usefully used in a lithium secondary battery.

1 is an EPMA (Electron Probe Micro-Analysis) result of particles after forming a first coating layer on a lithium transition metal oxide according to Example 1 (before forming a second coating layer).
FIG. 2 is a TEM (Transmission Electron Microscope) image of particles after forming a first coating layer on a lithium transition metal oxide according to Example 1 (before forming a second coating layer).
3 is a TEM (Transmission Electron Microscope) image of particles after forming a first coating layer on a lithium transition metal oxide according to Comparative Example 1 (before forming a second coating layer).
4 is an X-ray photoelectron spectroscopy (XPS) result of the positive active material on which the first coating layer and the second coating layer are formed according to Example 1. FIG.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In this specification, terms such as "comprise", "comprising" or "have" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or numbers It is to be understood that it does not preclude in advance the possibility of the presence or addition of steps, components, or combinations thereof.

Hereinafter, the present invention will be described in more detail.

In the present invention, the 'primary particle' refers to the smallest particle unit that is distinguished into one lump when the cross section of the positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of one crystal grain, or a plurality of It may be made up of crystal grains.

In the present invention, the average particle diameter of the primary particles is the arithmetic average of the values measured by the Image J program for each primary particle size that is distinguished from the cross-sectional SEM image of the positive active material particles obtained using a scanning electron microscope (SEM). is the value

In the present invention, 'secondary particles' means a secondary structure formed by aggregation of a plurality of primary particles.

In the present invention, the average particle diameter (D ₅₀ ) of the secondary particles is a particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle diameter (D ₅₀ ) of the secondary particles may be obtained using a laser diffraction method. Specifically, the average particle diameter (D ₅₀ ) of the secondary particles is obtained by dispersing the positive active material particles in a dispersion medium (ex. distilled water) and then introducing the particles into a laser diffraction particle size measuring device (Microtrac S3500) when the particles pass through the laser beam. In the particle size distribution curve obtained by measuring the diffraction pattern difference according to the particle size, it is the particle size at the point where it becomes 50% of the volume accumulation amount.

cathode active material

The cathode active material according to the present invention may include a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium; a first coating layer formed on the surface of the secondary particles of the lithium transition metal oxide and some or all of the plurality of primary particles, containing nickel and manganese, and having a layered structure; and a second coating layer formed on the outer surface of the first coating layer and containing boron.

The positive active material according to the present invention is in the form of secondary particles in which a plurality of primary particles are aggregated, and may include a lithium transition metal oxide having a nickel content of 80 atm% or more among metal elements other than lithium.

Specifically, the lithium transition metal oxide contained in the positive electrode active material of the present invention may have a composition represented by the following formula (1).

[Formula 1]

Li _a Ni _b Co _c M ¹ _d M ² _e O ₂

In Formula 1, M ¹ may be one or more selected from Mn and Al, and preferably Mn or a combination of Mn and Al.

In Formula 1, M ² is one selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y may be more than one species.

A represents the molar ratio of lithium in the lithium transition metal oxide, and may be 0.9≤a≤1.3, 0.9≤a≤1.2, or 1.0≤a≤1.1.

b represents the molar ratio of nickel among metal elements other than lithium in the lithium transition metal oxide, and may be 0.80≤b<1.0, 0.80≤b≤0.98, or 0.80≤b≤0.95. When the nickel content satisfies the above range, high capacity characteristics may be realized.

Where c represents the molar ratio of cobalt among metal elements other than lithium in the lithium transition metal oxide, and may be 0<c≤0.2, 0<c≤0.15, or 0.01≤c≤0.10.

d represents the molar ratio of M ¹ among metal elements other than lithium in the lithium transition metal oxide, and may be 0<d≤0.2, 0<d≤0.15, or 0.01≤d≤0.10.

The e represents the molar ratio of M ² among metal elements other than lithium in the lithium transition metal oxide, and may be 0≤e≤0.1, or 0≤e≤0.05.

The lithium transition metal oxide contained in the positive electrode active material of the present invention may have an average particle diameter of primary particles of 0.1 μm to 0.5 μm, preferably 0.1 μm to 0.3 μm. When the average particle diameter of the primary particles satisfies the above range, sufficient capacity of the secondary battery may be secured.

The lithium transition metal oxide contained in the positive electrode active material of the present invention may have an average particle diameter (D ₅₀ ) of the secondary particles of 8 μm to 15 μm, preferably 9 μm to 12 μm. When the average particle diameter (D ₅₀ ) of the secondary particles is smaller than the above range, there is a problem in that the gas reaction due to a side reaction with the electrolyte in the manufactured secondary battery increases too much, and the average particle diameter (D ₅₀ ) of the secondary particles is If it is larger than the above range, there is a problem in that the electrode current collector is torn when the positive electrode active material is coated on the electrode.

The positive electrode active material according to the present invention is formed on the surface of secondary particles of lithium transition metal oxide and some or all of the plurality of primary particles, contains nickel and manganese, and includes a first coating layer having a layered structure can do.

Since the first coating layer has a layered structure and has the same crystal structure as lithium transition metal oxide, it is considered that the stability and initial charge/discharge characteristics of the positive electrode active material can be improved compared to the coating layer having a spinel structure.

The first coating layer may be formed on the surface of the lithium transition metal oxide secondary particles and on the surface of some or all of the plurality of primary particles inside the secondary particles. The first coating layer may be formed to be connected to each other to fill all the gaps between the primary particles. Preferably, the first coating layer is formed on the surfaces of all of the plurality of primary particles, and may be formed to fill all the gaps between the primary particles.

The average thickness of the first coating layer may be 10 nm to 200 nm, preferably 30 nm to 100 nm. When the average thickness of the first coating layer satisfies the above range, by suppressing the occurrence of cracks at the interface between the primary particles, stability and initial capacity may be improved.

The first coating layer according to the present invention may include manganese and nickel. By including the manganese and nickel, the first coating layer according to the present invention may have a layered structure, thereby improving the stability and initial charge/discharge characteristics of the positive electrode active material compared to the coating layer having a spinel structure containing only manganese. I think.

The first coating layer according to the present invention may include lithium-nickel manganese oxide by diffusion of lithium in lithium transition metal oxide during heat treatment.

Specifically, the first coating layer may have a composition represented by the following Chemical Formula 2.

[Formula 2]

Li _x Ni _y Mn _z O ₂

The x represents the molar ratio of lithium in the first coating layer, and may be 0.8≤x≤1.2, preferably 1.00≤x≤1.02.

The y represents the molar ratio of nickel in the first coating layer, and may be 0.1≤y≤0.9, preferably 0.2≤y≤0.8.

The z represents the molar ratio of manganese in the first coating layer, and may be 0.1≤z≤0.9, preferably 0.2≤z≤0.8.

Specifically, the molar ratio of nickel to manganese included in the first coating layer may be 1:9 to 9:1, preferably 5:5 to 9:1, more preferably 6:4 to 8:2. can When the molar ratio of nickel to manganese included in the first coating layer is less than 1:9, sufficient initial charge/discharge capacity cannot be obtained because the first coating layer has a spinel structure. When the molar ratio of nickel:manganese included in the first coating layer is greater than 9:1, the nickel content is high and the capacity retention rate is lowered, and thus cycle characteristics may be undesirable.

The first coating layer according to the present invention may be included in an amount of 1 to 5 parts by weight, preferably 1 to 3 parts by weight, more preferably 1.5 to 2.5 parts by weight based on 100 parts by weight of the lithium transition metal oxide. may be included as a part. When the content of the first coating layer satisfies the above range, the stability and initial capacity may be improved by suppressing the occurrence of cracks at the interface between the primary particles.

The positive active material according to the present invention is formed on the outer surface of the first coating layer, and may include a second coating layer containing boron. The first coating layer having the layered structure may improve the problem of deterioration of initial charge/discharge characteristics, which is a disadvantage of the coating having a spinel structure, but a phenomenon in which cycle characteristics are deteriorated appears. Accordingly, cycle characteristics may be improved by forming a second coating layer containing boron on the outer surface of the first coating layer having a layered structure.

Specifically, in the second coating layer according to the present invention, in this case, the second coating layer may contain boron in the form of an amorphous boron compound such as lithium boron oxide and boron oxide. For example, the second coating layer is LiBO ₂ , Li ₂ B ₄ O ₇ , LiB ₃ O ₅ , B ₂ O ₃ and the like. The amorphous boron compound can be continuously coated in the form of a film, an island, or a mixture thereof, unlike the crystalline compound that can only be discontinuously coated in the form of particles.

The second coating layer may be included in an amount of 0.01 part by weight to 1 part by weight, preferably 0.05 part by weight to 0.5 part by weight, more preferably 0.1 part by weight to 0.3 part by weight based on 100 parts by weight of the lithium transition metal oxide. have. When the content of the second coating layer satisfies the above range, cycle characteristics may be improved.

In the cathode active material according to the present invention, the content of lithium by-products remaining on the surface may be 1 wt% or less, specifically, 0.6 wt% or less, based on the total weight of the cathode active material.

Method for manufacturing positive active material

The method for manufacturing a positive active material according to the present invention comprises the steps of: preparing a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium; A first heat treatment is performed after mixing the lithium transition metal oxide with a solution containing a nickel raw material and a manganese raw material, and the surface of the secondary particles of the lithium transition metal oxide and some or all of the plurality of primary particles Forming a first coating layer containing nickel and manganese on the surface, and having a layered structure; and mixing the lithium transition metal oxide on which the first coating layer is formed with a boron raw material, and performing a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer.

First, it is possible to prepare a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium.

The lithium transition metal oxide may be used by purchasing a commercially available product, or may be prepared using a method for preparing a lithium transition metal oxide known in the art. For example, the lithium transition metal oxide may be prepared by mixing a lithium raw material and a cathode active material precursor and then sintering.

The cathode active material precursor may be, for example, represented by the following [Formula A] or [Formula B].

[Formula A]

[Ni _p Co _q M ¹ _r M ² _s ](OH) ₂

[Formula B]

[Ni _p Co _q M ¹ _r M ² _s ]O OH

In Formulas A and B, M ¹ may be one or more selected from Mn and Al, and preferably Mn or a combination of Mn and Al.

In Formulas A and B, M ² is Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y from the group consisting of It may be one or more selected.

The p denotes a molar ratio of nickel among the metal elements in the precursor, and may be 0.80≤p<1.0, 0.80≤p≤0.98, or 0.80≤p≤0.95.

The q denotes a molar ratio of cobalt among the metal elements in the precursor, and may be 0<q≤0.2, 0<q≤0.15, or 0.01≤q≤0.10.

The r denotes a molar ratio of the M ¹ element among the metal elements in the precursor, and may be 0<r≤0.2, 0<r≤0.15, or 0.01≤r≤0.1.

The s denotes a molar ratio of the M ² element among the metal elements in the precursor, and may be 0≤s<0.1, or 0≤s≤0.05.

The lithium raw material is, for example, lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH·H ₂ O), lithium hydroxide anhydride (LiOH), LiNO ₃ , CH ₃ COOLi and Li ₂ (COO) ₂ It may be at least one selected from the group consisting of, preferably lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH·H ₂ O), or a combination thereof.

When preparing the cathode active material, the cathode active material precursor and the lithium raw material may be mixed so that a molar ratio of Li:transition metal is 1:1 to 1.3:1, preferably 1:1 to 1.1:1. When the mixing ratio of the cathode active material precursor and the lithium raw material satisfies the above range, the crystal structure of the cathode active material is smoothly developed, and a cathode active material having excellent physical properties can be manufactured. When the content of the lithium raw material is too small, the crystal structure is not properly developed, and when the content of the lithium raw material is too large, unreacted Li remains as a by-product, which may cause a decrease in capacity and generation of gas.

Meanwhile, the sintering may be performed at a temperature of 700°C to 1000°C, preferably 700°C to 900°C, and more preferably 700°C to 850°C. When the calcination temperature is less than 700° C., the raw material remains in the particles due to insufficient reaction, which may reduce the high-temperature stability of the battery, and the bulk density and crystallinity may decrease, resulting in poor structural stability. On the other hand, when the sintering temperature exceeds 1000°C, non-uniform growth of particles may occur, and it may be difficult to disintegrate the particles, thereby reducing capacity.

The calcination may be performed for 5 hours to 24 hours, preferably for 10 hours to 24 hours. If the calcination time is less than 5 hours, the reaction time may be too short to obtain a highly crystalline positive active material, and if it exceeds 24 hours, the particle size may become excessively large, and production efficiency may be reduced.

When the cathode active material is manufactured by the manufacturing method according to the present invention, since the lithium by-product on the surface of the lithium transition metal oxide is consumed during the formation of the first coating layer and the second coating layer, a lithium transition metal oxide that has not been washed with water is used. Even so, the residual amount of lithium by-products in the finally manufactured positive electrode active material is small. Specifically, the content of the lithium by-product remaining on the surface of the cathode active material according to the present invention may be 1 wt% or less, specifically, 0.6 wt% or less, based on the total weight of the cathode active material. Therefore, the step of preparing the lithium transition metal oxide of the present invention may not include a water washing process. As described above, according to the method for manufacturing a high-nickel positive electrode active material according to the present invention, the washing process can be omitted, thereby solving the problems caused by the washing process and reducing equipment and process costs.

Next, a first heat treatment is performed after mixing the prepared lithium transition metal oxide with a solution containing a nickel raw material and a manganese raw material, and the surface of the secondary particles of the lithium transition metal oxide and some of the plurality of primary particles Alternatively, a first coating layer containing nickel and manganese and having a layered structure may be formed on the entire surface.

Specifically, in the step of forming the first coating layer, for example, a solution containing a lithium transition metal oxide, a nickel raw material and a manganese raw material is mixed, stirred, and separated by filtration, followed by preparation in an oxygen atmosphere. 1 It can be carried out by a method of heat treatment.

In the step of forming the first coating layer, a solution containing a nickel raw material and a manganese raw material penetrates into the primary particle interface inside the lithium transition metal oxide, so that the first coating layer is coated on the primary particle interface as well as the secondary particles. think it could be For this reason, in the cathode active material according to the present invention, crack generation between primary particles is suppressed, thereby improving high-temperature cycle characteristics.

The nickel raw material and the manganese raw material are each 0.5 parts by weight to 10 parts by weight, preferably 1 part by weight to 8 parts by weight, more preferably 2 parts by weight to 8 parts by weight based on 100 parts by weight of the lithium transition metal oxide can be mixed as much as possible. The amounts of the nickel raw material and the manganese raw material are adjusted so that the formed first coating layer is included in an amount of 1 to 5 parts by weight based on 100 parts by weight of the lithium transition metal oxide in the positive electrode active material. When the content of the nickel raw material and the manganese raw material satisfies the above ranges, the stability and initial capacity may be improved by suppressing the occurrence of cracks at the interface between the primary particles.

As the nickel raw material, for example, nickel acetate, nickel sulfate, nickel chloride, nickel nitrate, and the like may be used.

As the manganese raw material, for example, manganese acetate, manganese sulfate, manganese chloride, manganese nitrate, etc. may be used.

Meanwhile, a solution including the nickel raw material and the manganese raw material may be prepared by dissolving the nickel raw material and the manganese raw material in a solvent such as water or ethanol.

When lithium transition metal oxide is added to the solution containing the nickel raw material and the manganese raw material and stirred, the nickel and manganese contained in the solution are attached to the surface of the lithium transition metal oxide.

After separation by filtration, a first heat treatment is performed to obtain a lithium transition metal oxide powder having a first coating layer.

At this time, the filtration may be performed by putting filter paper in a filtration flask and vacuum reducing the pressure, and the drying is at 50°C to 200°C, preferably at 80°C to 150°C for 2 hours to 20 hours, preferably for 5 hours. It can be carried out for 15 hours to 15 hours.

The first heat treatment is for forming a first coating layer by fixing nickel and manganese on the surface of the lithium transition metal oxide, and may be performed at a temperature of 650°C to 850°C, preferably at a temperature of 650°C to 750°C. . When the heat treatment temperature is less than 650° C., a first coating layer having a spinel structure rather than a layered structure is obtained. On the other hand, when the heat treatment temperature exceeds 850°C, the particle strength is excessively increased due to inter-particle necking, so a process of additionally densely pulverizing the particle agglomerates must be added during the subsequent process, or the capacity at the time of charging and discharging when manufacturing a secondary battery There is a problem with this falling.

The first heat treatment may be performed for 1 hour to 10 hours, preferably for 3 hours to 7 hours. When the heat treatment time is within the above range, an appropriate first coating layer may be formed and production efficiency may be improved.

Through the above process, when the first coating layer is formed, the lithium transition metal oxide on which the first coating layer is formed is mixed with a boron raw material, and a second heat treatment is performed to form a second coating layer containing boron on the outer surface of the first coating layer. can be formed

Specifically, the forming of the second coating layer may be performed by dry mixing a boron raw material such as boric acid with the lithium transition metal oxide on which the first coating layer is formed, followed by a second heat treatment.

When the second coating layer is formed on the first coating layer, it is possible not only to improve the deterioration of cycle characteristics due to the formation of the first coating layer, but also to lower the movement barrier energy of lithium ions by the constituent element boron. In addition, since the generated second coating layer suppresses a direct reaction between the electrolyte and lithium transition metal oxide, the stability of the positive electrode active material and the lifespan characteristics of the secondary battery to which the positive active material is applied may be improved.

The boron raw material may be a powder including amorphous compound particles including boron. For example, boric acid, _B2O3 , etc. are mentioned _.

The boron raw material may be mixed so that 0.0001 parts by weight to 10 parts by weight, preferably 0.001 parts by weight to 5 parts by weight, more preferably 0.01 parts by weight to 1 parts by weight, respectively, based on 100 parts by weight of the lithium transition metal oxide. have. The amount of the boron raw material is adjusted so that the formed second coating layer is included in an amount of 0.01 part by weight to 1 part by weight based on 100 parts by weight of lithium transition metal oxide in the positive electrode active material. When the content of the boron raw material satisfies the above range, the direct reaction between the electrolyte and the lithium transition metal oxide may be suppressed to improve the stability of the positive electrode active material and the lifespan characteristics of the secondary battery to which the positive electrode active material is applied.

The second heat treatment is to form a second coating layer by fixing the boron-containing compound attached to the outer surface of the first coating layer of the lithium transition metal oxide on which the first coating layer is formed, and at a temperature of 150° C. to 500° C., preferably 300° C. It may be carried out at a temperature of from 400 °C. When the heat treatment temperature is less than 150° C., it is impossible to coat because it is below the melting point of the boron-containing compound. On the other hand, when the heat treatment temperature exceeds 500 ℃, there is a problem that the coating is not well because the boron layer is crystallized.

The second heat treatment may be performed for 1 hour to 10 hours, preferably for 3 hours to 7 hours. When the heat treatment time is within the above range, an appropriate second coating layer may be formed and production efficiency may be improved.

Meanwhile, the second heat treatment is preferably performed in an oxygen atmosphere.

By the second heat treatment, a second coating layer containing boron is formed on the outer surface of the first coating layer. In this case, the second coating layer may contain boron in the form of an amorphous boron compound such as lithium boron oxide or boron oxide. For example, the second coating layer is LiBO ₂ , Li ₂ B ₄ O ₇ , LiB ₃ O ₅ , B ₂ O ₃ and the like.

anode

The positive electrode according to the present invention includes the above-described positive electrode active material of the present invention. Specifically, the positive electrode includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material according to the present invention. Since the positive active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be specifically described below.

The positive electrode current collector may include a metal having high conductivity, and the positive electrode active material layer is easily adhered, but is not particularly limited as long as it has no reactivity in the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

The positive electrode active material layer may optionally include a conductive material and a binder, if necessary, together with the positive active material.

At this time, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight based on the total weight of the positive active material layer, and excellent capacity characteristics when included in the above content range can indicate

The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and the like, and any one of them or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive active material layer.

The binder serves to improve adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (≤VDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl Methacrylate (polymethymethaxrylate), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene -diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca, or various thereof copolymers, and the like, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, the positive electrode is prepared by dissolving or dispersing the above-described positive electrode active material and optionally a binder, a conductive material, and a dispersing agent in a solvent on the positive electrode current collector, followed by drying. and rolling, or casting the composition for forming a positive electrode active material layer on a separate support, and then laminating a film obtained by peeling from the support on a positive electrode current collector.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), dimethylformamide (dimethyl formamide, DMF), acetone or water may be mentioned, and one type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is to dissolve or disperse the positive electrode active material, the conductive material, the binder, and the dispersant in consideration of the application thickness of the slurry and the production yield, and then to have a viscosity that can exhibit excellent thickness uniformity when applied for manufacturing the positive electrode. That's enough.

electrochemical device

Next, an electrochemical device according to the present invention will be described. The electrochemical device according to the present invention includes the positive electrode of the present invention described above, and the electrochemical device may specifically be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is the same as described above, so detailed description is omitted, Hereinafter, only the remaining components will be described in detail.

In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0<β<2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

The anode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the anode active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the anode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetra fluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the anode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the anode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The negative electrode is prepared by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on the negative electrode current collector, or the composition for forming the negative electrode active material layer It can be prepared by casting on a separate support and then laminating a film obtained by peeling it from this support on a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and if it is used as a separator in a lithium secondary battery, it can be used without any particular limitation, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles, such as R-CN (R is a C2-C20 linear, branched, or cyclic hydrocarbon group, and may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as an anion of the lithium salt, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be at least one selected from the group consisting of, The lithium salt is, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) _2. LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and lifespan characteristics, so portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle, HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin type.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source for a small device, but can also be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

Examples of the medium-large device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Example 1

A lithium transition metal oxide having a composition of LiNi _0.86 Co _0.05 Mn _0.07 Al _0.02 O ₂ and having a secondary particle form in which a plurality of primary particles are aggregated was prepared.

50 g of the lithium transition metal oxide was added to a solution in which 3.96 g of nickel nitrate and 1.06 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (nickel: manganese in solution = 8:2), and at 100° C. for 1 hour After mixing, it was dried in an oven at 130°C. Then, the dried resultant was subjected to a first heat treatment at 750° C. in an oxygen atmosphere to form a first coating layer.

After mixing 30 g of the resultant formed with the first coating layer and 0.18 g of boric acid powder, a second heat treatment was performed in an air atmosphere at a temperature of 300° C. for 5 hours to form a second coating layer, and then the sintered body was pulverized and classified to obtain a cathode active material for a lithium secondary battery. obtained.

Example 2

A first coating layer was formed by adding the lithium transition metal oxide to a solution (molar ratio of nickel: manganese in solution = 6:4) in which 2.97 g of nickel nitrate and 2.12 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (DI water). Except for that, a positive active material was prepared in the same manner as in Example 1.

Example 3

A first coating layer was formed by adding the lithium transition metal oxide to a solution (molar ratio of nickel: manganese in solution = 4:6) in which 1.98 g of nickel nitrate and 3.18 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (DI water). Except for that, a positive active material was prepared in the same manner as in Example 1.

Example 4

A first coating layer was formed by adding the lithium transition metal oxide to a solution of 0.99 g of nickel nitrate and 4.24 g of manganese nitrate in 15.0 g of ultrapure water (nickel: manganese in solution = 2:8). Except for that, a positive active material was prepared in the same manner as in Example 1.

Comparative Example 1

A cathode active material was prepared in the same manner as in Example 1, except that the lithium transition metal oxide was added to a solution in which only 5.29 g of manganese nitrate was dissolved in 15.0 g of ultrapure water (DI water) to form a first coating layer.

<Structural analysis of the first coating layer>

1 is an EPMA (Electron Probe Micro-) for particles after forming a first coating layer according to Example 1 (before forming a second coating layer) on lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated; Analysis) result. In FIG. 1, a manganese-rich (Mn-rich) region was observed at the interface of the primary particles. Through this, it can be confirmed that the raw materials injected to form the first coating layer on the primary particle interface are coated to form the first coating layer.

2 is a TEM (Transmission Electron Microscope) image of the particles after forming the first coating layer (before forming the second coating layer) according to Example 1. The image indicated by 1 in FIG. 2 is an image of lithium transition metal oxide, and the image indicated by 2 in FIG. 2 is an image of the first coating layer. In the images indicated by 1 and 2 of FIG. 2 , a Fast Fourier Transfrom (FFT) pattern observed in both the layered structure was observed, and it was confirmed that both the lithium transition metal oxide and the first coating layer of Example 1 had a layered structure.

FIG. 3 is a TEM (Transmission Electron Microscope) image of particles after forming a first coating layer (before forming a second coating layer) on a lithium transition metal oxide, which is a secondary particle, according to Comparative Example 1; 3A is an image of the first coating layer. In the image indicated by A in FIG. 3, an FFT pattern of a spinel structure was observed. That is, it was confirmed that the first coating layer of Comparative Example 1 had a spinel structure.

<Analysis of whether the second coating layer contains boron>

4 is an X-ray photoelectron spectroscopy (XPS) result of the positive active material on which the first coating layer and the second coating layer are formed according to Example 1. FIG. As shown in the graph of FIG. 4 , it was confirmed that boron was contained in the second coating layer located on the outermost surface of the positive electrode active material.

<Measurement of primary particle and secondary particle size>

The primary particle average particle diameter of the lithium transition metal oxides used in Examples 1 to 4 and Comparative Example 1 was measured using SEM, and the lithium transition metal oxides used in Examples 1 to 4 and Comparative Example 1 using laser diffraction method. of secondary particle average particle diameter (D ₅₀ ) was measured.

As a result of the measurement, the average particle diameter of the primary particles was 0.15 μm, and the average particle diameter (D ₅₀ ) of the secondary particles was 10 μm.

<Measurement of content of second coating layer>

ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) analysis was performed to measure the content of boron contained in the second coating layer of Example 1.

As a result of inverse calculation of the content of lithium boron oxide or boron oxide contained in the second coating layer from the content of boron obtained as a result of the measurement, in Example 1, the content of the second coating layer was 0.1% by weight based on 100 parts by weight of the lithium transition metal oxide was calculated as

<Measurement of average thickness of first coating layer>

The thickness of the first coating layer of Example 1 was measured using a TEM image. Specifically, in the positive electrode active material of Example 1, the thickness of the first coating layer was obtained by observing arbitrary three locations by TEM, and an average value thereof was calculated.

As a result of the measurement, in Example 1, the average thickness of the first coating layer was measured to be 80 nm.

Experimental Example 1 - Measurement of the content of lithium by-products remaining on the surface of the positive electrode active material

The content of the lithium by-product remaining on the surface of each of the positive active materials prepared in Examples 1 to 4 was measured.

Specifically, 5 g of the positive active material prepared in Examples 1 to 4 and Comparative Example 1 was stirred in 100 mL of ultrapure water for 5 minutes, filtered, and the filtered solution was titrated with 0.1 N HCl. After obtaining a titration curve using a Metrohm pH meter, equivalence points of LiOH and Li ₂ CO ₃ were obtained from the titration curve to calculate the content of lithium byproducts remaining on the surface of the positive electrode active material. The results are shown in Table 1 below.

For comparison, the content of lithium by-products remaining on the surface of the lithium transition metal oxide before forming the first coating layer in Examples 1 to 4 is shown in Table 1 together.

Residual amount of Li ₂ CO ₃
(weight%) Residual amount of LiOH
(weight%) Total content of lithium by-products
(weight%) Example 1 0.09 0.43 0.52 Example 2 0.09 0.39 0.48 Example 3 0.09 0.34 0.43 Example 4 0.09 0.33 0.42 lithium transition metal oxide 1.23 0.60 1.83

Referring to Table 1, it can be seen that the positive electrode active materials of Examples 1 to 4 have sufficiently reduced residual lithium even though they do not undergo a water washing process.

Experimental Example 2 - Initial discharge capacity evaluation

92.5 wt% of each of the positive active materials prepared in Examples 1 to 4 and Comparative Example 1, 3.5 wt% of carbon black as a conductive material, and 4 wt% of polyvinylidene fluoride as a binder were mixed in N-methylpyrrolidone solvent Thus, a positive electrode slurry was prepared. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130° C., and then rolled to prepare a positive electrode.

An electrode assembly was prepared by using a Li metal as a counter electrode of the positive electrode and interposing a porous PE separator between the positive electrode and the negative electrode. Place it inside the case and inject an electrolyte mixed with ethylene carbonate (EC)/ethylmethylcarbonate (EMC)/diethylcarbonate (DEC) in a volume ratio of 3:4:3 to the coin-shaped halves A battery was prepared.

Each of the batteries prepared as described above was charged to 4.25V at 25°C with a constant current of 0.1C, and then discharged to 3.00V with a constant current of 0.1C, and the initial discharge capacity was measured. The results are shown in Table 2 below.

initial charge capacity
(mAh/g) Initial discharge capacity
(mAh/g) Example 1 225.35 198.61 Example 2 223.95 193.99 Example 3 222.48 188.69 Example 4 218.30 184.61 Comparative Example 1 217.46 184.99

Referring to Table 2, it can be seen that the secondary battery to which the positive active material of Examples 1 to 4 is applied has a higher initial discharge capacity than the secondary battery to which the positive active material of Comparative Example 1 is applied.

Experimental Example 3 - Cycle Characteristics Evaluation

Each of the batteries prepared in Experimental Example 2 was charged to 4.25V at 45°C with a constant current of 0.33C and discharged to 3.00V at a constant current of 0.33C as one cycle, after 30 cycles of charging and discharging, after 30 cycles The capacity retention rate compared to the initial dose was measured. The results are shown in Table 3 below.

Capacity retention rate (%) Example 1 97.07 Example 2 95.15 Example 3 94.78 Example 4 92.88 Comparative Example 1 91.16

Referring to Table 3, it can be seen that the secondary batteries to which the positive active materials of Examples 1 to 4 are applied have superior high-temperature cycle characteristics compared to the secondary batteries to which the positive active materials of Comparative Example 1 are applied.

Claims (21)

lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium;
a first coating layer formed on the surface of the secondary particles of the lithium transition metal oxide and some or all of the plurality of primary particles, containing nickel and manganese, and having a layered structure; and
A positive electrode active material formed on the outer surface of the first coating layer, comprising a second coating layer containing boron. According to claim 1,
The lithium transition metal oxide is a cathode active material having a composition represented by the following formula (1):
[Formula 1]
Li _a Ni _b Co _c M ¹ _d M ² _e O ₂
In Formula 1,
M ¹ is at least one selected from Mn and Al,
M ² is at least one selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y,
0.9≤a≤1.3, 0.8≤b<1.0, 0<c≤0.2, 0<d≤0.2, 0≤e≤0.1. The method of claim 1,
An average particle diameter of the primary particles is 0.1 μm to 0.5 μm. According to claim 1,
The secondary particles have an average particle diameter (D ₅₀ ) of 8 μm to 15 μm. According to claim 1,
The first coating layer has an average thickness of 10 nm to 200 nm. According to claim 1,
The first coating layer is a cathode active material having a composition represented by the following Chemical Formula 2:
[Formula 2]
Li _x [Ni _z Mn _w ] _y O ₂
In Formula 2, 0.8≤x≤1.2, 0.8≤y≤1.2, 0.1≤z≤0.9, and 0.1≤w≤0.9. According to claim 1,
A positive electrode active material having a molar ratio of nickel to manganese included in the first coating layer of 1:9 to 9:1. According to claim 1,
A cathode active material having a molar ratio of nickel to manganese included in the first coating layer of 5:5 to 9:1. According to claim 1,
The first coating layer is a cathode active material that is included in an amount of 1 to 5 parts by weight based on 100 parts by weight of the lithium transition metal oxide. According to claim 1,
The second coating layer is a cathode active material comprising at least one selected from the group consisting of lithium boron oxide and boron oxide. According to claim 1,
The second coating layer is a cathode active material that is included in an amount of 0.01 parts by weight to 1 part by weight based on 100 parts by weight of the lithium transition metal oxide. According to claim 1,
A positive active material in which the content of lithium by-products remaining on the surface is 1% by weight or less based on the total weight of the positive active material. Preparing a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium;
A first heat treatment is performed after mixing the lithium transition metal oxide with a solution containing a nickel raw material and a manganese raw material, and the surface of the secondary particles of the lithium transition metal oxide and some or all of the plurality of primary particles Forming a first coating layer containing nickel and manganese on the surface, and having a layered structure; and
Mixing the lithium transition metal oxide on which the first coating layer is formed with a boron raw material, and performing a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer. 14. The method of claim 13,
The step of preparing the lithium transition metal oxide,
A method for producing a cathode active material, which is performed by mixing a lithium raw material and a cathode active material precursor and then calcining. 14. The method of claim 13,
The preparing of the lithium transition metal oxide is a method of manufacturing a positive electrode active material that does not include a water washing process. 14. The method of claim 13,
The raw material for nickel is nickel nitrate, and the raw material for manganese is manganese nitrate. 14. The method of claim 13,
The first heat treatment is a method of manufacturing a cathode active material that is carried out at 650 ℃ to 850 ℃. 14. The method of claim 13,
The boron raw material is a method of manufacturing a positive electrode active material of boric acid. 14. The method of claim 13,
The second heat treatment is a method of manufacturing a positive electrode active material that is carried out at 150 ℃ to 500 ℃. A positive electrode comprising the positive active material of any one of claims 1 to 12. A lithium secondary battery comprising the positive electrode of claim 20, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

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